FIGURE 6.

Looping Transition: (Top) Time series of in-plane and out-of-plane motion for windows of 6.7 s (as in Fig. 3). Formation of a LacR-mediated DNA loop decreases the effective tether length and thereby decreases the motion as evidenced with the transition seen at t = 190 s with recovery at t = 240 s. (Bottom) Time series of average displacement for each dimension (again using 6.7 s windows and corrected for linear drift). In contrast to Fig. 3, there are no distinct shifts in the in-plane displacement and therefore no change in the anchor point. This indicates that the transitions seen in the top panel are internal to the tether and do not involve the coverslip surface, a finding that is consistent with DNA looping. Microsphere diameter = 560 nm, tether length = 1.5 kbp.